#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=2e5+1000;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL a[1<<20];
bool vis[1<<20];
priority_queue< LL ,vector<LL> ,greater<LL> >que;
int main(void){
   cin.tie(0);std::ios::sync_with_stdio(false);
   LL n;cin>>n;
   for(LL i=1;i<=n;i++){
      cin>>a[i];
   }
   for(LL i=0;i<=18;i++){
      vis[1<<i]=1;
   }
   LL ans=0;
   for(LL i=n;i>=1;i--){
      if(a[i]==-1) break;
      else{
         que.push(a[i]);
         if(vis[i]){
            ans+=que.top();
            que.pop();
         }
      }
   }
   cout<<ans<<"\n";
   return 0;
}
